This invention relates to a soy protein product with a modified sugar profile. The soy protein product has desirable flavor and functional properties. The soy protein product has a high sucrose and monosaccharide content and is low in indigestible oligosaccharides. The soy protein product does not have galactinol that is present in soybeans developed to have a low indigestible oligosaccharide content. The soy protein product is rich in isoflavones. The method for manufacturing the soy protein product uses conventional soybeans that have better agronomic properties than soybeans developed to have a low indigestible oligosaccharide content. The method for manufacturing the soy protein product uses a xcex1-galactosidase enzyme. The method for manufacturing the soy protein product retains the natural level of isoflavones occurring in soybeans.
This invention relates to a soy protein product. The benefits of soy protein are well documented.
Cholesterol is a major concern with consumers throughout the industrialized world. It is well known that vegetable products contain no cholesterol. For decades, nutritional studies have indicated that the inclusion of soy protein in the diet actually reduces serum cholesterol levels in people who are at risk. The higher the cholesterol, the more effective soy proteins are in lowering that level.
Soybeans have the highest protein content of all cereals and legumes with around 40% protein while other legumes have 20-30%, whereas cereals have about 8-15% protein. Soybeans also contain about 20% oil and the remaining dry matter is mostly carbohydrate (35%). On a wet basis (as is), soybeans contain about 35% protein, 17% oil, 31% carbohydrates and 4.4% ash.
In the soybean, both storage protein and lipid bodies are contained in the usable meat of the soybean (called the cotyledon). The complex carbohydrate (or dietary fiber) is also contained in the cell walls of the cotyledon. The outer layer of cells (called the seed coat) makes up about 8% of the soybean""s total weight. The raw, dehulled soybean is, depending on the variety, approximately 18% oil, 15% soluble carbohydrates, 15% insoluble carbohydrates, 14% moisture and ash and 38% protein.
In processing, soybeans are carefully selected for color and size. The soybeans are then cleaned, conditioned (to make removal of the hull easier) and cracked, dehulled and rolled into flakes. The flakes are subjected to a solvent bath that removes the oil. The solvent is removed and the flakes are dried, creating the defatted soy flakes that are the basis of all soy protein products. Despite the large number of products on the market, there are only three types of soy protein: flours, isolates and concentrates.
Soy flours are the simplest forms of soy protein with a protein content of approximately 50%. Simply grinding and screening the defatted flakes produces soy flours.
Soy flours are high in oligosaccharides, the soluble carbohydrates that give soy flours the xe2x80x9cbeanyxe2x80x9d flavor that some people find objectionable. The simple processing leaves the soy flour with many of the soybean""s characteristics. The lack of processing also makes soy flours highly variable in terms of quality.
Soy flours and grits are still widely produced and are used most often in baked goods, snack foods and pet foods applications where the high flavor profile does not pose a problem. Textured soy flours were an early attempt at simulating or enhancing the texture of meat products. Texturizing does not change the composition of soy flours and reduces the flavor profile only slightly. Their primary applications are inexpensive meat products or pet foods.
The oligosaccharides raffinose and stachyose in soy flour potentially cause flatulence as their bacterial fermentation in the colon creates intestinal gas. Suarez reported that ingestion of 34 grams (g) of conventional soy flour (1.3 g raffinose and stachyose) caused no significant increase in flatulence frequency, whereas ingestion of 80 g of conventional soy flour (3.1 g raffinose and stachyose) resulted in a significant increase in flatulence frequency. xe2x80x9cGas Production in Humans Ingesting a Soybean Flour Derived from Beans Naturally Low in Oligosaccharides,xe2x80x9d Suarez, Fabrizis L. et al., Am. J. Clin. Nutr., 69:135-9 (1999).
The prior art describes methods for reducing the oligosaccharide content of soy milk and soy flour. Crocco describes using xcex1-galactosidase from microbial or fungal sources as a means for pre-digesting oligosaccharides in soy milk. xe2x80x9cTreatment of Soy Milk Oligosaccharides by a Homogeneric Enzyme Extract Containing xcex1-Galactosidase,xe2x80x9d Crocco, Stephanie Carmela, The Louisiana State University and Agricultural and Mechanical College (1973); Food Technology, Order No. 74-18, 329. Mulimani describes attempting to use a crude preparation of xcex1-galactosidase from guar to degrade oligosaccharides present in soybean flours. xe2x80x9cEnzymatic Degradation of Oligosaccharides in Soybean Flours,xe2x80x9d Mulimani, H. V. et al., Food Chemistry, Vol. 59, No. 2, pp. 279-282 (1997). Ultrafiltration has also been employed to remove the oligosaccharides from soy milk.
Isolates are produced through standard chemical isolation, drawing the protein out of the defatted flake through solubilization (alkali extraction at pH 7-10) and separation followed by isoelectric precipitation. As a result, isolates are 90% protein on a moisture-free basis. Isolates can be made with a high percentage of soluble protein and a low flavor profile. They contain no dietary fiber and are sometimes high in sodium, properties that can limit their application. Isolate processing is relatively complex and much of the soybean""s protein is lost in the centrifuging process, so the cost of isolates is high. Their major applications have been in dairy substitution, as in infant formulas and milk replacers.
Soy concentrates have at least 65% protein and typically have about 70% protein. A myriad of applications has been developed for soy concentrates and texturized concentrates in processed foods"" meat, poultry, fish, cereal and dairy systems.
Removing soluble carbohydrate material from defatted soy meal makes soy protein concentrates. Aqueous alcohol extraction (60-80% ethanol) or acid leaching (isoelectric pH 4.5) is the most common means for carbohydrate removal.
The prior art describes soy protein products made from low oligosaccharide soybeans. In U.S. Pat. No. 5,858,449, Crank describes a process for making a soy protein product that has at least 60% protein and 10% sucrose and less than 4% dietary fiber and 1.5% stachyose. In U.S. Pat. No. 5,936,069, Johnson describes a process for making a soy protein product having at least 60% protein and less than 3% stachyose, 1% raffinose and 0.5% fiber. Crank uses soybeans that have a low stachyose content due to mutagenesis techniques. Johnson uses soybeans genetically modified to have a low raffinose and stachyose content.
It is an object of this invention to make a novel, soy protein product with a modified sugar profile from soybeans conventionally grown by farmers and used by soybean processors. The modified sugar profile results in desirable flavor and functional properties.
It is further an object of this invention to produce a soy protein product with a desired level of sucrose. A high sucrose content gives the soy protein product advantages of sweetness and nonbrowning over conventional soy.
It is further an object of this invention to produce a soy protein product with a combined sucrose and monosaccharide content as great as the sucrose content of products made from low oligosaccharide soybeans. Monosaccharide is similar to sucrose in sweetness.
It further is an object of this invention to produce a soy protein product that is low in indigestible oligosaccharides. It is further an object of this invention to be able to control the manufacturing process to achieve a desired, reduced oligosaccharide content.
It was discovered that the sucrose and indigestible oligosaccharide content of the soy protein product can be controlled by using a single activity enzyme that hydrolyses only stachyose and raffinose to generate galactose and sucrose. The prior art does not teach a soy protein product made from conventional soybeans. The prior art also does not teach using an enzymatic process to make a soy protein product.
It is further an object of this invention to make a soy protein product by an economically efficient method. The low oligosaccharide soybeans used by Crank and Johnson tend to have poorer agronomic properties than conventional soybeans. Agronomic properties include germination and seedling development, growing and maturity, nitrogen fixation, disease and pest resistance and yield. The low oligosaccharide soybeans used by Crank and Johnson also would have higher harvesting, drying, storage, marketing, trading, handling and processing costs because the soybeans must be segregated and identity preserved.
It is further an object of this invention to make a soy protein product that does not contain galactinol. The low oligosaccharide soybeans used by Crank and Johnson contain galactinol. Suarez reported that the low oligosaccharide soy flour had about 2.2% galactinol, whereas soy flour from conventional soybeans had none, as conventional soybeans do not contain a detectable amount of galactinol. It is believed that galactinol, a precursor in raffinose and stachyose synthesis, also would cause intestinal gas by fermentation in the colon. Therefore, the potential digestibility benefits of low oligosaccharide soybeans might be negated by the presence of galactinol in that soybean.
It is further an object of this invention to produce a soy protein product that is rich in isoflavones. In recent years, isoflavones have been researched extensively to better understand their role in chronic disease prevention. The American Institute for Cancer Research says isoflavones xe2x80x9cmay inhibit enzymes necessary for the growth and spread of many types of cancer,xe2x80x9d such as breast cancer, prostate cancer and colon cancer. And isoflavones are also showing great promise in preventing osteoporosis and treating menopausal symptoms. Isoflavones are largely unaffected by the invention""s water extraction process. Therefore, they are retained in the invention at naturally occurring levels found in soybeans.
It is further an object of this invention to produce a soy protein product containing significant amounts of calcium, magnesium, phosphorus, potassium and amino acids. These nutritional constituents are largely unaffected by the invention""s water extraction process. Therefore, they are retained in the invention at naturally occurring levels found in soybeans.
The present invention comprises a soy protein product having (a) at least 60% protein of total dry matter; (b) a combined sucrose and monosaccharide content of at least 10% of total dry matter and (c) less than about 5% indigestible oligosaccharides of total dry matter and (d) being substantially free of galactinol. In another embodiment, this invention concerns a method for manufacturing a protein product comprising: (a) providing a substantially defatted soybean material; (b) treating said material with an enzyme at an effective temperature and pH for an effective time to achieve a combined sucrose and monosaccharide content of at least 10% of total dry matter in said product and less than 5% indigestible oligosaccharides of total dry matter in said product; (c) removing fiber from said material before or after said treatment to achieve at least 60% protein of total dry matter in said product and (d) inactivating said enzyme after said treatment. The product is then used in a liquid or dry beverage, food or nutritional product.